The present invention relates to a subframe for a motor vehicle having two side plates which extend in the longitudinal direction of the vehicle and have bearings for control arms of wheel suspension links. The side plates each are torsion-proof and rigid lattice frames which extend in a vertical longitudinal plane of the vehicle. The side plates have integrated bearings in the side plates for control arms of wheel suspension links, and top and bottom chords. Torsion-proof cross members are each separately connectable to the side plates in a detachable manner. The cross members are held between the side plates to connect the side plates and form a rigid assembly subframe unit with the side plates.
A subframe for a front axle of a motor vehicle for the coupling of suspension links is known from the German Patent Document DE-A 12 78 855, in which side plates are connected with cross members, and a fixedly connected structural unit is formed. The use of such a subframe is contemplated for one vehicle type only and cannot be used for vehicle types of different constructions and driving conceptions.
It is an object of the present invention to provide a subframe which, with respect to the construction, can be adapted in a simple manner to differently constructed vehicle types as well as driving and operating systems and ensures an economical assembly during manufacturing as well as for repair purposes.
This and other objects are achieved by the present invention which provides a subframe for a motor vehicle having two side plates which extend in the longitudinal direction of the vehicle and having bearings for control arms of wheel suspension links. The side plates each are torsion-proof and rigid lattice frames which extend in a vertical longitudinal plane of the vehicle. The side plates have integrated bearings in the side plates for control arms of wheel suspension links, and top and bottom chords. Torsion-proof cross members are each separately connectable to the side plates in a detachable manner. The cross members are held between the side plates to connect the side plates and form a rigid assembly subframe unit with the side plates. The assembly subframe unit is detachably fastened on a body of the vehicle via one bearing respectively in the top and bottom chords of the side plate. The bearings are arranged in spaced horizontal planes.
Advantageously, the subframe comprises detachably assembled structural elements, such as side plates and cross members. In comparison to undetachably connected elements according to the state of the art, this makes it possible for the subframe to be used in vehicles of different conceptions in that only the cross members are exchanged and in that the subframe can be adapted to the local situations of the vehicle body or of the drive unit or to a vehicle with rear wheel steering. For this purpose, the side plates are provided with corresponding fastening capability for cross members that can connected locally in various manners.
Together with the cross members, the side plates of the subframe form a rigid assembly unit. They have integrated bearing receiving devices for the wheel suspension. Together with the connected wheel suspension links, these side plates form a so-called preassembly unit which, after the connection with the cross members, is a final assembly unit which, for example, in series production on the assembly line, can be connected with the vehicle body. With this type of assembly, it is also advantageous that the corresponding adjustments of the axle can be carried out before the mounting into the vehicle.
In a preferred embodiment, the side plates are made from cast aluminum in a light-weight construction and each have connecting upright struts between a bottom chord and a top chord, an opening forming between these struts and the chords which, in the case of driven rear wheels, is used for the guiding-through of a drive shaft and which is situated centrically with respect to the wheel spin axis.
On the forward free end of the bottom chord and at the rearward free end of the top chord, bearings for the fixing on the vehicle body can be inserted. These are provided approximately at the same longitudinal distance to the wheel spin axis so that the same transversal or lateral forces are introduced into the subframe bearings. On the connecting line of the two bearings, the wheel spin axis is also situated which has the advantage of a low introduction of moments into the subframe.
The bearings have a defined elastic characteristic in the longitudinal, transverse and vertical direction.
The cross members of the subframe are designed corresponding to the vehicle type, for example, with a rearward drive assembly or with a forward drive assembly and a rearward differential gear, the side plates being usable for each of these vehicle types in an unchanged state. The linking of the cross members takes place in junction points of the side plates. As a function of the vehicle with a rearward drive assembly or the vehicle with the forward drive assembly and the rear axle differential gear, the cross member will then be constructed correspondingly either as a bridge member or as a cross member with a center bearing for the differential gear which is preferably situated in a neutral zone where the slightest movements occur. The differential gear is supported on the subframe only in this one bearing. The additional bearing may be provided directly on the vehicle body or on a support of the vehicle with a relatively large base so that only moderate forces are introduced into the subframe in the vertical direction and mainly no overturning moment is introduced into the subframe, as would be the case if the two bearings for the holding of the rear axle differential gear according to the state of the art were arranged on the subframe.
Also, for a vehicle with additional rear wheel steering and independently of the position of the drive assembly, a different rearward cross member is used than for a vehicle having only front wheel steering. With additional rear wheel steering, a cross member is used in which a corresponding operating cylinder for the steering is arranged, or the operating cylinder is integrated into the cross member, in which case, the operating cylinder will then be connected on each end with an oblong console which is screwed to the side plate. Without any deflection, the tie rod applied to the wheel carrier is guided through the console and is connected with the piston rod by way of a joint. The cross member has a partially cornered cross section and is designed corresponding to the loads to be absorbed.
In certain preferred embodiments, the consoles are constructed to be non-resistant to bending and twisting which permits the predominant keeping-away of forces acting on the operating cylinders. For achieving a compact construction of the cross member unit comprising the integrated operating cylinder with the rear wheel control element, the latter is connected directly with the housing of the operating cylinder or with the cross member, either in front or behind the cross member as viewed in the driving direction.
As described above, the cross members are constructed to be adapted to the respective vehicle type. Thus, it is necessary, in the case of a rear drive unit that a relatively large space is created in the vertical direction that is free from the cross member. This is advantageously achieved by a bridge member which spans the drive unit and which, by means of its downwardly directed legs, is fastened to the side plate by screws which extend in the longitudinal direction of the vehicle. A compensating of tolerances will become possible as a result.
For the economical manufacturing of the bridge member, the bridge member comprises two identical parts which are connected with one another in an articulated manner in the center in the area of the transversely extending supporting webs by a pin. The bridge member has a light-weight construction and, for this purpose, has webs which connect the upper and the lower chord, are arranged in the manner of a lattice construction and form openings between one another.
The cross members either have a round cross section or comprise a ribbed casting in the form of a U-profile or a double-T-profile, or have a polygonal construction and are made of a light metal or another light material. The linking to the side plates takes place by connecting flanges on the ends of the cross members. These are welded on or are connected with the cross member in another manner. The construction of the subframe as an assembly unit comprising detachable side plates and cross members has the advantage of an exchangeability of all parts in the case of repair. Furthermore, in a simple manner, a power unit or assembly may be demounted by the removal of a lower cross member, in which case the wheel suspension remains unchanged so that there will be no suspension alignment.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.